Frequency-controllled phase shift oscillator



y 6 G. L. COLLINS ET AL 3,254,311

FREQUENCY-CONTROLLED PHASE SHIFT OSCILLATOR Filed Dec. 4, 1962 P28 OEVI/CE 6Z4 INVENTORS 64?! A. COLL/NI BY 52/1 51? M NEAJO/V United States Patent 3,254,311 FREQUENCY-CONTROLLED PHASE SHIFT OSCILLATOR Gary L. Collins, Los Angeles, and Ernest V. Nelson, Long Beach, Calif, assignors to G. L. Collins Corp, Long Beach, Calif, a corporation of California Filed Dec. 4, 1962, Ser. No. 242,125 Claims. (Cl. 331-65) The present invention relates to means and techniques for determining movements and positions and involves generally the use of a position-towoltage or current transducer to control the frequency of an oscillatory circuit in accordance wit-h such transducer.

Briefly, as described herein, there is provided a phase shift oscillatory circuit in which a signal derived from a transducer is combined to alter phase conditions in the oscillatory circuit and thereby control the frequency of oscillations, the resulting frequency of oscillations then being a measure of a position or movement sensed by the transducer. The system disclosed also includes adjustable circuitry for compensating for phase shift in the particular transducer used such that either small or short-stroke transducers may be incorporated in the system. The system may also include an adjustment for establishing a predetermined midfrequency from which frequency deviations may be effected by the transducer, this adjustment being desirable in those instances where the present system is used in conjunction with a telemetering system or the like having the corresponding frequency to which the present system may be adjusted. The system disclosed also may use nonlinear resistances such as a lamp bulb for achieving voltage regulation functions in the system.

It is therefore a general object of thepresent invention to provide systems of this character having the aboveindicated features, functions and producing the above indicated results.

A specific object of the present invention is to provide a system of this character using a phase-shift oscillator in which phase conditions within the oscillator may be altered by a transducer to effect a change in frequency of the resulting oscillations.

Another specific object of the present invention is to provide a system of this character incorporating adjustable means whereby the system may be adapted for use with different transducers for operation in conjunction with an associated system having a predetermined frequency about which frequency deviations may be accomplished by the transducer.

Another specific object of the present invention is to provide a system of this character incorporating nonlinear devices such as a lamp bulb for regulatory purposes.

Another specific object of the present invention is to provide a system of this character in which the transducer is advantageously coupled into the oscillatory circuit such as to accomplish a minimum loading effect on dew'ces in the oscillatory circuit.

Another specific object of the vpresent invention is to provide specific electrical circuitry for accomplishing these desired features, functions and results. I

Another specific object of the present invention is to provide a system of this character in which the output voltage is substantially a sine wave, substantially free of harmonics and distortions.

3,254,311 Patented May 31, 1966 Another specific object of the present invention is to provide a system of this character which avoids the necessity of filtering or shaping circuits which would otherwise result in a slower response in the output signals to changed conditions of the transducer.

Another specific object of the present invention is to provide a system of this character cap-able of many different uses, not only for detecting displacement or movement but also, for example, pressure and acceleration and other conditions since it will be seen that the transducer may be associated with or be a bellows, Bourd-on tube or spring mass system.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. This invention itself, both as to its organization and manner of operation, together with further objects and advantages thereof, may be best understood by reference to the following description taken in connection with the accompanying drawings in which:

FIGURE 1 illustrates generally a system embodying features of the present invention.

FIGURE 2 illustrates specific circuitry used in the system of FIGURE 1; and

FIGURE 3 illustrates a modified system also embodying features of the present invention.

Referring to the generalized form of system illustrated in FIGURE 1, the same inclddes a phase-shift-type oscillator having a first phase-shifting stage 10, a second phaseshifting stage 11, an amplifier stage 12, and a feedback connection 14 extending from the output terminal 15 to the input terminal 116 of the first phase-shifting stage 10. In accordance with features of the present invention, a mechanical-to-electrical transducer 17, illustrated in the form of a differential transformer, has its primary winding 19 connected to the output circuit of amplifier 12 and its secondary winding 20, comprising two oppositely wound sections 20A and 203, coupled to a point 22 intermediate the phaseashifting stages 10 and 11 for purposes of introducing a quadrature, i.e. one displaced degrees, for purposes of altering the phase conditions in the oscillator and thus the frequency of the voltage appearing at the output terminal 15.

The transducer 17 has a movable core member 24 which cooperates magnetically with the primary and secondary windings 19, 20 and which is mechanically coupled, as indicated by the dotted line 26, to a device 28 whose position'or movement is being sensed.

The output voltage, represented as E and derived from terminal 15, is applied to an indicator or utilization means 30 for purposes either of indicating the frequency of the output voltage E or using the same as, for example, in telemetering systems as a subcarrier or modulation component of either an amplitude or a frequency-modulated wave. One feature of the present system is that the amplitude of the voltage E remains substantially constant and changes are effected only in its frequency.

The impedances 32 and 33 in FIGURE 1, respectively in the feedback path 14 and in the circuit coupling the secondary of the transducer 17 to the stage 11, are illustrated in generalized form and their specific nature may be seen from the following description of FIGURES 2 and 3.

Referring to FIGURE 2, the phase-shifting networks 10 and 11 of FIGURE 1 include, respectively, transistors a.) fill and 51 each having its collector electrode connected through corresponding resistances 52 and 53 to the nega tive voltage lead -1 and each having its emitter electrode connected to the grounded lead 55 through corresponding resistances 56 and 57, the lead 54 being connected to the negative terminal of DC. source 58 having its other terminal grounded. The base electrode of transistor is connected to the point 16 in a voltage-dividing circuit comprising resistances 6t) and 61 which are connected in series between the leads 54 and for establishing essentially the bias on the base electrodes of transistors 51), 51, 64 and 65 through resistance connections which are presently described.

The emitter electrode of transistor 50 is connected to the base electrode of transistor 5'1 through, in turn, resistance 67, resistance 68 and the adjustable tap 69A on potentiometer-type resistance ea. A capacitor 7%, for phase-splitting purposes, is connected, between on the one hand, the junction point of resistances 67 and 68 and, on the other hand, to the collector electrode of transistor 5h, this junction point being identified by the reference numeral 72.

The emitter electrode of transistor 51 is connected through resistance 72A to the base electrode of transistor 64 and for phase-splitting purposes a capacitor 74 is connected between the collector electrode of transistor 51 and the base electrode of transistor 64. The collector elec trode of transistor 64 is directly connected to the base electrode of transistor 65 and also to the negative lead 54 through resistance 76, the emitter electrode of transistor 64 being connected to the grounded lead 55 through resistance 77.

The transistor 65', functioning as an emitter follower, has its collector electrode connected directly to the negative lead 54 and its emitter electrode returned to ground through resistance 79.

The transistor 88, functioning as an amplifier, has its collector electrode connected to the negative lead 54 through the outside terminals of potentiometer-type resistance 2 and the emitter electrode of such transistor is returned to ground through, in turn, the two series-connected resistances 84 and 85. The base electrode of transistor is connected to the point 87 in a voltagedividing circuit comprising, in turn, the resistance 96, lamp bulb 91 and resistance 92 connected between the negative lead and grounded lead 55. It is noted that the point 87 is the junction point between light bulb Q1 and resistance 2 and that a capacitor 94 is connected between the emitter electrode of transistor 65 and the junction point of resistance W and light bulb 91.

A feedback voltage is derived from the junction point of resistances S4 and and the same is coupled to the base electrode of transistor 51) through capacitor 7 and feedback lead 14.

The primary winding 19 of transducer 17 has one of its terminals grounded. and the other one of its terminals coupled to the emitter electrode of transistor 81 through coupling capacitor 95 which serves also to prevent the flow of DC. to the primary winding 19. The secondary winding 2h has its output connected across the series-connectcd resistances 63 and 69.

For purposes of explaining the operation of the system shown in FIGURE 2, it is assumed that the phase of the oscillations produced at point 16, i.e. at the base of transistor 5%", is of Zero phase. Correspondingly, the phase at the emitter of transistor 59 is of zero phase and the signal on the collector of transistor 50 has a ISO-degree phase, and these two signals on the emitter and collector are combined at point '72 to have a 90-degree phase. Considering for the moment that the output of the secondary winding 2% is zero, i.e. the core 2 5 is in its rnidposition between equal coil sections ZilA and 2013, the signal on the base of transistor 51 has a 90-degree phase and, correspondingly, the phases of the signal on the emitter and collector electrodes of transistor 51 are 90 degrees and 270 degrees, respectively, which, when combined by the resistance 72A and capacitor '74, results 1n a signal of ISO-degree phase being applied to the base electrode of amplifier 64. For these purposes, the capacitors 7t) and 74 have equal values and also the resistances 6'7 and 72A have equal values. The frequency of oscillation is established by these values and may be such that, for example, the nominal frequency of operation may be 10,000 cycles per second. The signal appearing on the collector of transistor 64 may then be considered to have a zero phase as is also the signal developed on the emitter of the emitter follower transistor 65. The phase of the signal applied to the base of transistor amplifier 8t) is also zero as is also the signal developed on its emitter which is applied through the feedback lead 14 to the base electrode of transistor 59.

The phase relationship at the base of transistor 51 is altered when a signal is developed in the secondary winding 211. Such signal developed in secondary winding 20 and applied to the series-connected resistances 68 and 69 has either a zero-degree phase or a ISO-degree phase, depending upon the position of the core member 24. This signal of either zero-degree phase or ISO-degree phase is in guadrature, i.e. in 90-degree relationship with respect to the assumed 90-degree phase signal at point 72. Hence, there is a vectorial addition or combining of signals that results in a change in frequency of oscillations such as to automatically reestablish a difference in phase of degrees of the oscillations at point 16 and at the base electrode of transistor 64. A useful output voltage appearing on the tap 82A of the resistance 82 is applied to the utilization means 30 through coupling capacitor 97.

In a set adjusted position of tap 82A, the amplitude of the signal applied to the utilization means 30 remains substantially constant even though its frequency changes, the amplitude remaining substantially constant as a result of the operation of the regulating circuit involving the light bulb 91. In this respect it will be seen that the base electrode of transistor 80 is connected in a signal voltagedividing circuit that comprises light bulb 1 and resistance 92. When the signal applied to such voltage-dividing circuit tends to rise, a greater current flows through the light bulb 91 and resistance 92 to increase the value of the resistance of the light bulb 91 and thereby result in a lowering of the signal voltage across resistance 92 which is connected between the base and emitter electrodes of transistor '80. Conversely, when the signal tends to decrease in amplitude, the value of the resistance of bulb 91 decreases and a larger proportion of the signal voltage is applied between the base and emitter electrodes of transistor 80, thereby maintaining the output voltage applied to the utilization means 30 substantially constant.

The arrangement shown in FIGURE 3 is a modification and refinement of the system in FIGURE 2 in that it employs additional emitter follower stages for better impedance matching purposes, and includes two adjustable means, one serving to adjust the midfrequency of operation and the other serving to adjust or compensate for phase shift in different ones of transducers which may be used.

In FIGURE 3 the phase-shifting stages 10 and. 11, corresponding to the stages 10 and 11 in FIGURES 1 and 2, comprise respectively transistors 1% and 101 each having its collector electrode connected to the positive lead 102 through corresponding resistances 103 and 1M and each having its emitter connected to the grounded lead 1% through corresponding resistances 107 and 108. In this case the base electrode of transistor 1% is returned to the lead 182 through transistor 1311. Specifically, the base electrode of transistor lllil is connected to one terminal of resistance 108A having its other terminal connected through feedback lead 14 to one terminal of. each of resistance 1519 and light bulb 1119 at junction point 111. A potentiometer-type resistance 112 interconnects the other terminals of resistance 109 and light bulb 110 and the junction point 113 of light bulb 110 and resistance 112 is connected to the grounded lead 106 through resistance 115. The emitter electrode of transistor 100 is connected to the base electrode of transistor 101 through the series-connected resistances 117 and 118 having their junction point 119 coupled through capacitor 120 to the collector electrode of transistor 100.

The collector and emitter electrodes of transistor 101 are respectively coupled to the base electrode of transistor 122 through capacitor 123 and resistance 124. The capacitors 120 and 123 are of equal values as are also the resistances 117 and 124 and the transistor 122 functions as an emitter follower offering a high input impedance to the output of the transistor 101 to minimize its loading. The collector of transistor 122 is connected directly to the positive lead 102 and the emitter electrode is connected to the base electrode of transistor 124 and also to the grounded lead 106 through resistance 125.

The transistor 124, functioning as an amplifier, has its collector electrode connected to the positive lead 102 through resistance 127 and has its emitter electrode connected to the grounded lead 106 through resistance 128.

Transistor 130 has its 'base electrode connected directly to the collector electrode of transistor 124, its collector electrode connected to the positive lead 102 through resistance 132 and its emitter connected to the grounded lead 196 through the previously mentioned resistance 115. Feedback voltage to the base of transistor 100 is derived from both the collector and emitter electrodes of transistor 130 and for that purpose the collector of transistor 130 is coupled to the junction point of resistances 109 and 112 through capacitor 134 at junction point 135 and the emitter of transistor 130 is connected to thejunction point 113.

The useful output signal is derived from the junction point 113 which is connected to the base electrode of the emitter follower transistor 137 having its collector electrode connected to the positive lead 102 and its emitter electrode connected to the grounded lead 106 through the potentiometentype resistance 138. The tap 138A on resistance 138 is coupled to the utilization means 140 through capacitor 141.

The voltage appearing across resistance 138 is applied to the primary winding 19 through the coupling and blocking capacitor 142. The secondary winding 20 of transducer 17 having the movable core member 24. is connected across the outside terminals of the potentiometer-type resistance 143 having one of its terminals grounded. The tap 143A on resistance 143 is coupled through capacitor 145 to the base electrode of transistor 146, such base electrode being connected in a voltagedividing circuit which includes the resistances 147 and 148 connected between the positive lead 102 and ground. Transistor 146 has its collector connected to the positive lead 102 through resistance 149 and has its emitter electrode connected to ground through resistance 150 and functions as a phase splitter. The collector electrode of transistor 146 is coupled to the base electrode of transistor 152 through capacitor 153 and the emitter electrode of transistor 146 is coupled to the base electrode of transistor 152 through the adjustable resistance 155. The transistor 152 functions as an emitter follower and has its collector electrode connected to the positive lead 102 and its emitter electrode returned to ground through resistance 157, such emitter being coupled to the junction point 22 through resistance 160. It is also noted that the adjustable tap 112A on resistance 112 is coupled to the same junction point 22 through the resistance 162 for effecting a combination of signals at such junction point 22.

Analyzing the system shown in FIGURE 3, it is noted that the same includes two additional phase-shifting networks, one involving the transistor 130 and the other involving the transistor 146, with the first-mentioned phase- 6 adjust the nominal or midfrequency of operation, such tap 112A being adjusted either with the core member 24 in its central position or with the deviation control tap 143A on resistance 143 being at ground potential. The second mentioned phase shifter, involving the transistor 146 and the adjustable tap 155A on resistance 155, serves to provide compensation for phase shift in various transof different electrical and physical characteristics.

The output voltage applied to the utilization means 140 is maintained substantially constant by automatic changes in the resistance of the light bulb which, as in FIG- URE 2, is connected in a voltage-dividing circuit that functions to provide a smaller proportion-ate voltage between the base and emitter electrodes of transistor 137 when the output voltage tends to rise and, conversely, to apply a larger proportionate voltage between these elements when the output voltage tends to decrease as a result of increased feedback voltage. In this respect it is noted that the voltage-dividing circuit mentioned includes the light bulb 110 and resistance and the same are connected between the feedback lead 14 and ground.

Comparing FIGURES 2 and 3, it will be seen that adjustments of the taps 69A and 143A are forv the same general purpose, namely for adjusting the amount of, frequency shift produced per unit voltages developed in the corresponding secondary windings 20 in that both taps 69A and 143A serve to adjust the amplitude of an amplified or gain signal which is vectorially added with the oscillator signal appearing at junction point 72 in FIGURE 2 and at junction point 119 in FIGURE 3. In each case the oscillator signal is of much larger amplitude than the gain signal, largely because of the differential connection of the secondary winding sections 20A and 20B, and in each case the oscillator signal and gain signal stand in quadrature relationship to each other, i.e. in 90-degree phase relationship to each other. While in FIGURE 2 only two signals are combined for effecting a phase shift, in FIGURE 3 a third signal derived from the tap 112A is combined for adjustment of the nominal or midfrequency point of operation as described above. This third signal, derived from the tap 112A in FIGURE 3, for reference purposes, is termed a gain frequency adjustment signal in contrast to the signal developed in secondary winding 20 which is termed a gain unbalance signal. Both of these gain signals are introduced in FIGURE 3 into the oscillator loop circuit for combination with the oscillator loop signal such as to effect a phase change and consequently a change in oscillation frequency.

In each case it wfll be seen that under the assumed conditions above, the phase of the oscillator loo-p signal at points 72 in FIGURE 2 and 22 in FIGURE 3 each have a 90-degree phase and the gain signals or signal which is combined therewith has either a zero-degree phase or a ISO-degree phase. When the gain signal has a Zerodegree phase, the oscillator frequency is increased and when the gain signal has a ISO-degree phase, the oscillator signal is decreased, the amount of frequency change in the oscillator being proportional to the amplitude of the gain signal. The frequency changes in each case such as to make the oscillator loop gain unity for sustain ing oscillations.

The stability of the oscillator is determined primarily by the quality of the capacitor components 70 and 74 and 123) and resistances 67 and 72 (resistances 117 and 124) which are used in the two 90-degree phase splitters or shifters.

Another advantage of this particular system is that it is relatively insensitive to changes in power supply voltage since the frequency of oscillations is determined mainly by phase shift and not necessarily by a particular value of supply voltage.

Using relatively small gain voltages in comparison with the loop voltages which are combined therewith, a good linear relationship between frequency and transducer output voltage is obtained when the gain signal is relatively small in comparison to the oscillator loop Signal with which such gain signal is combined. In those instances where the linearity between frequency and transducer position requires improvement, then a nonlinear transducer may be used having an output which varies as the antilog of position. In those instances where the relationship between transducer position and output voltage is linear, the log of the output frequency may be made to vary proportionately with respect to transducer displacement.

In FIGURES 2 and 3, the various resistance and capacitance elements may have the following values in ohms and micro-farads:

74 .05 97 50 108A 3,300 103 1,800 107 1,800 117 and 1124- are equal.

larger than 110 112 10,000 143 10,000 14-7 18,000 148 3,300 149 1,800 150 1,800 10,000 157 1,800 160 3,300 162 560 120 and 123 are equal.

While the particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

We claim:

1. An oscillator having an input circuit and an output circuit, a phase-sensitive network connected between said input and output circuits, said network incorporating means for amplifying a signal applied to said input circuit and appearing in amplified form in said output circuit, means forming a positive feedback circuit between said input and output circuits, a position transducer comprising a transformer having one of its windings coupled to said output circuit and a second one of its windings coupled to said phase-sensitive network for altering the frequency of oscillations in said output circuit.

2. An oscillator circuit having an input circuit'and an output circuit with a positive feedback path extending therebetween, said oscillator including a second path between said input circuit and said output circuit in which there is a pair of phase-shifting means for successively phase-shifting a signal in said oscillator through ninety degrees with the signal at a point intermediate said pair of phase-shifting means being shifted ninety degrees with respect to the phase of said output circuit, said second path including amplifying means for amplifying a signal applied in said input circuit and appearing at said output circuit in amplified form, a position transducer coupled between said output circuit and said point and effective to alter the phase condition at said point and thereby alter the frequency of oscillations.

3. An oscillator circuit having an input circuit and an output circuit and a positive feedback path extending therebetween, said oscillator circuit including a second path having a first ninety-degree phase-shifting network coupled to said input circuit, said second path having a second ninety-degree phase-shifting network coupled to said first network at a phase-sensitive point which controls the frequency of oscillations, said second path including means coupling said second network to said output circuit, said second path including amplifying means for amplifying a signal applied in said input circuit and appearing at said output circuit in amplified form, a transformer having one of its windings coupled to said output circuit and a second one of its windings coupled between a terminal of said output circuit and said phase-sensitive point, said transformer having a movable element which changes the relation between said windings to thereby alter the frequency of oscillations, and frequenc -sensitive utilization means coupled to said oscillator circuit.

4. A system as set forth in claim 3 in which said coupling means includes a pair of transistors, one of said transistors having its base and emitter electrodes coupled to said second network, a source of voltage having its terminals connected between the emitter and collector electrodes of said one transistor, 2; voltage-dividing circuit connected between said terminals and comprising a nonlinear resistance, the other of said transistors having its emitter and base electrodes coupled between different spaced points on said voltage divider circuit, the emitter electrode of said one transistor being coupled through said nonlinear resistance to the base electrode of said other transistor and the collector electrode of said other transistor being coupled to said output circuit.

5. A system as set forth in claim 3 including nonlinear means in said coupling means and coupled to said output circuit and functioning in response to changes in output oscillator voltage for producing a substantially constant output oscillator voltage.

6. A system as set forth in claim 3 including adjustable means in said coupling means for adjustment of the nominal operation frequency of the oscillator.

7. A system as set forth in claim 3 including adjustable means coupled to said transformer for adjustment of the frequency deviation produced by said transformer.

8. A system as set forth in claim 3 including an adjust able phase-shifting network coupling said transformer between said point and said output circuit for compensating for different phase conditions in said transformer.

9. A system as set forth in claim 3 including first adjustable phase-shifting means in said coupling means and coupled between said output circuit and said point for adjustment of the frequency of said oscillator circuit, and second adjustable phase-shifting means coupling said transformer between said output circuit and said point for compensating for difierent phase conditions in said transformer.

10. A system as set forth in claim 9 including a nonlinear resistance in said coupling means and coupled to 10 References Cited by the Examiner v UNITED STATES PATENTS 2,749,441 6/1956 Kelly 33l 183 X 3,046,535 7/1962 Philbin et al. 330-29 X 3,096,488 7/1963 Lomask 330 100 X FOREIGN PATENTS 1,015,580 10/1952 France.

759,573 10/1956 Great Britain.

ROY LAKE, Primary Examiner.

JOHN KOMINSKI, Examiner. 

1. AN OSCILLATOR HAVING AN INPUT CIRCUIT AND AN OUTPUT CIRCUIT, A PHASE-SENSITIVE NETWORK CONNECTED BETWEEN SAID INPUT AND OUTPUT CIRCUITS, SAID NETWORK INCORPORATING MEANS FOR AMPLIFYING A SIGNAL APPLIED TO SAID INPUT CIRCUIT AND APPEARING IN AMPLIFIED FORM IN SAID OUTPUT CIRCUIT, MEANS FORMING A POSITIVE FEEDBACK CIRCUIT BETWEEN SAID INPUT AND OUTPUT CIRCUITS, A POSITION TRANSDUCER COMPRISING A TRANSFORMER HAVING ONE OF ITS WINDINGS COUPLED TO SAID OUTPUT CIRCUIT AND A SECOND ONE OF ITS WINDINGS COUPLED TO SAID PHASE-SENSITIVE NETWORK FOR ALTERING THE FREQUENCY OF OSCILLATIONS IN SAID OUTPUT CIRCUIT. 